An LED (light emitting diode) is widely put to practical use and mainly used in applications for optical transmission, display and special illumination as an element having a p-n junction of compound semiconductor. In recent years, a white light LED using nitride semiconductors and phosphors is also put to practical use and it is highly expected to expand into an application for generic illumination in the future. However, in case of the white LED, because energy conversion efficiency is inadequate compared to an existing fluorescent bulb, a major efficiency improvement is necessary for a generic illumination application. Furthermore, there are still many problems for an achievement of an LED having a low cost and high luminous flux. As a white light LED on the market now, it comprising a blue light emitting diode element mounted on a lead frame, a yellow phosphor layer which consists of YAG:Ce and is covered on this blue light emitting diode element, and a mold lens which consists of a transparent resin of an epoxy resin etc. and covers them is known. In case of this white LED, when blue light is emitted from the blue emitting diode element, a part of the blue light is converted to yellow light in passing through the yellow phosphor. Because blue light and yellow light have a relationship of complimentary colors each other, white light is made by mixing blue light and yellow light. In case of this white LED, a performance upgrade etc. of the blue light emitting diode element is required for an efficiency improvement and an advancement of color rendering properties.
As the blue light emitting diode element, it has a n-type SiC substrate on which a buffer layer consisting of AlGaN, a n-type GaN layer consisting of n-GaN, a multiple quantum well active layer consisting of p-AlGaN and a p-type contact layer consisting of p-GaN are continuously stacked in this order is known. Also, a p-side electrode is formed on a surface of the p-type contact layer and an n-side electrode is formed on a backside of the SiC substrate, and blue light is emitted from the multiple quantum well active layer when passing an electric current by applying a voltage between the p-side electrode and the n-side electrode. In this the blue light emitting diode element, unlike in case of a blue emitting diode element using a sapphire substrate, because the SiC substrate has a conductive property and the electrodes can be arranged on the upper side and the under side, a reduction of manufacturing processes, an in-plane uniformity property of the electric current, an efficient use of an emission area in a chip area etc. are achieved.
Furthermore, an emitting diode element which produces white light by itself is proposed (for example, see the patent literature 1). In this emitting diode element, a fluorescent SiC substrate having a first SiC layer doped B and N and a second SiC layer doped Al and N is used instead of the n-type SiC substrate of the blue emitting diode element described above, and near-ultraviolet light is emitted from the multiple quantum well active layer. The near-ultraviolet light is absorbed by the first SiC layer and the second SiC layer, and coverted to visible light which is from green light to red light in the first SiC layer and visible light which is from blue light to red light in the second SiC layer respectively. As a result, white light which is a high color rendering property and close to sun light is emitted from the fluorescent SiC substrate.